Flame dominated thermoacoustic instabilities in a system with high acoustic losses

Hoeijmakers, Maarten; Kornilov, Viktor; Arteaga, Inés López; Goey, de Lph Philip; Nijmeijer, Henk

doi:10.1016/j.combustflame.2016.03.009

Cited by 40 publications

(34 citation statements)

References 21 publications

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“…It has also been found that increased acoustic losses at the end of combustor may destabilize the combustion system due to intrinsic flame instability. A somewhat similar observation has been made in experimental study by Hoeijmakers et al [19]. The experiments suggest that as the acoustic reflections at the combustor boundaries decrease, the eigen-frequencies of the system becomes fully determined by intrinsic flame modes.…”

Section: Introductionsupporting

confidence: 82%

“…Acoustic modes can be also subdued due to reduced acoustic reflections from the combustor ends. However, since in this work we have not considered non-ideal end conditions, we can mention this scenario only as an educated guess supported by the findings of Hoeijmakers et al [19]. answered all the questions we aimed at within the framework of this setting.…”

Section: (Vi)mentioning

confidence: 81%

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Intrinsic flame instabilities in combustors: Analytic description of a 1-D resonator model

Mukherjee

Shrira

2017

Combustion and Flame

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The study is concerned with theoretical examination of thermo-acoustic instabilities in combustors and focuses on recently discovered 'flame intrinsic modes'. These modes differ qualitatively from the acoustic modes in a combustor. Although these flame intrinsic modes were intensely studied, primarily numerically and experimentally, the instability properties and dependence on the characteristics of the combustor remain poorly understood. Here we investigate analytically the properties of intrinsic modes within the framework of a linearized model of a quarter wave resonator with temperature and cross-section jump across the flame, and a linear n   model of heat release. The analysis of dispersion relation for the eigen-modes of the resonator shows that there are always infinite numbers of intrinsic modes present. In the limit of small interaction index n the frequencies of these modes depend neither on the properties of the resonator, nor on the position of the flame. For small n these modes are strongly damped. The intrinsic modes can become unstable only if n exceeds a certain threshold. Remarkably, on the neutral curve the intrinsic modes become completely decoupled from the environment. Their exact dispersion relation links the intrinsic mode eigen-frequency i  with the mode number i m and the time lag  :    21 ii mm        , where m =0, +/-1. The main results of the study follow from the mode decoupling on the neutral curve and include explicit analytic expressions for the exact neutral curve on the n   plane, and the growth/decay rate dependence on the parameters of the combustor in the vicinity the neutral curve. The instability domain in the parameter space was found to have a very complicated shape, with many small islands of instability, which makes it difficult, if not impossible, to map it thoroughly numerically. The analytical results have been verified by numerical examination.

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Section: Introductionsupporting

confidence: 82%

Section: (Vi)mentioning

confidence: 81%

Intrinsic flame instabilities in combustors: Analytic description of a 1-D resonator model

Mukherjee

Shrira

2017

Combustion and Flame

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“…Their stability is determined by the flame-model parameters only, though Hoeijmakers et al (2014) demonstrates that, even for subcritical values of the gain, an appropriate change in the reflection coefficients can still destabilise the system. Experimentally, instabilities have been observed for nearly anechoic conditions at the upstream inlet, with frequencies in good agreement with the theoretical predictions for ITA modes (Hoeijmakers et al 2016). In addition, Emmert et al (2016) showed that a stable system can be driven into instability, if excited at intrinsic frequencies.…”

Section: Introductionsupporting

confidence: 75%

Thermoacoustic interplay between intrinsic thermoacoustic and acoustic modes: non-normality and high sensitivities

2019

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This study analyses the interplay between classical acoustic modes and intrinsic thermoacoustic (ITA) modes in a simple thermoacoustic system. The analysis is performed using a frequency-domain low-order network model as well as a time-domain spatially discretised model. Anti-correlated modal sensitivities are found to arise due to a pairwise interplay between acoustic and ITA modes. The magnitude of the sensitivities increases as the interplay between the modes grows stronger. The results show a global behaviour of the modes linked to the presence of exceptional points in the spectrum. The time-domain analysis results in a delay-differential equation and allows the investigation of non-normal behaviour and its consequences. Pseudospectral analysis reveals that energy amplification is crucially linked to an interplay between acoustic and ITA modes. While higher non-orthogonality between two modes is correlated with peaks in modal sensitivity, transient energy growth does not necessarily involve the most sensitive modes. In particular, growth estimates based on the Kreiss constant demonstrate that transient amplification relies critically on the proximity of the non-normal modes to the imaginary axis. The time scale for transient amplification is identified as the flame time delay, which is further corroborated by determining the optimal initial conditions responsible for the bulk of the non-modal energy growth. The flame is identified as an active and dominant contributor to energy gain. The frequency of the optimal perturbation matches the acoustic time scale, once more confirming an interplay between acoustic and ITA structures. Flame-based amplification factors of two to five are found, which are significant when feeding into the acoustic dynamics and eventually triggering nonlinear limit-cycle behaviour.

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“…In addition, the frequency of 200Hz-mode does not change significantly with and without acoustic liner. The above phenomenon is highly similar to the feature of the intrinsic thermoacoustic instability mode (ITA mode), which has been shown by Hoeijmakers et al [40] and Silva et al [41].…”

Section: Rigid Wallsupporting

confidence: 80%

Suppression of Combustion Instabilities in a Premixed Swirl Combustor with Acoustic Liner

Xu¹,

Wang²,

Liu³

et al. 2019

Proceedings of Global Power &Amp; Propulsion Society

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Acoustic liner is one of effective passive control methods of combustion instabilities. This paper presents an experimental investigation about the suppression of the combustion instabilities using acoustic liners. A premixed swirling combustor was built and a specially designed acoustic liner was set at the downstream of the flame zone. Then, experiments of rigid wall, acoustic liner without and with tunable bias flow were carried out respectively. Furthermore, considering the viscous dissipation of airflow is temperature related, the temperature of the bias flow was adjusted in order to evaluate its effects on thermoacoustic instabilities. The bias flow was heated by electric taps before entering the acoustic liner in this rig. Results shows that the unstable Helmholtz mode could be triggered, and the oscillation amplitude grows with the increase of the bias flow Mach number, while the instability of 1/4 wavelength mode may be completely suppressed. Within the scope of the experiments, the unstable Helmholtz mode triggered by the bias flow can be attenuated by raising the bias flow temperature, while no substantial changes are observed about the quarter wave mode. These results are rarely reported in previous studies. Studying the effects of acoustic liner on combustion instabilities can provide useful knowledge regarding its application in real combustion systems. NOMENCLATURE V Volume flow rate (slm) Ф Equivalence ratio (-) Wc Combustion power (kW) T Temperature (K) τ Time delay Ma Mach number y Axis coordinate of the burner (mm) P′ Amplitude of acoustic pressure (Pa) f Freqency (Hz) acpr Acoustic pressure from COMSOL (Pa) SNR Signal to noise ratio slm Standard litre per minute (L/min)

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Flame dominated thermoacoustic instabilities in a system with high acoustic losses

Cited by 40 publications

References 21 publications

Intrinsic flame instabilities in combustors: Analytic description of a 1-D resonator model

Intrinsic flame instabilities in combustors: Analytic description of a 1-D resonator model

Thermoacoustic interplay between intrinsic thermoacoustic and acoustic modes: non-normality and high sensitivities

Suppression of Combustion Instabilities in a Premixed Swirl Combustor with Acoustic Liner

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